1. Field of the Invention
The present invention relates to a torsional vibration damping device for use in the drive train of a motor vehicle having at least two rotationally connected coaxial cover plates which rotate about an axis of rotation within a certain angular range relative to a coaxial part located between the cover plates.
2. Description of the Related Art
Torsional vibration dampers are required to damp the rotational vibrations fundamentally occurring in internal combustion engines. These rotational vibration generate droning noises in the vehicle body and also generate noises in the downstream gearbox and differential of the vehicle. The elastic forces typically used to accept the rotational vibration and deliver a torque which is as even as possible must, on the one hand, be sufficiently small for effective damping and, on the other hand, must accept high accelerations or forces. A large rotational deflection and therefore a large angle of twist between the two relatively rotatable parts are therefore desirable in the torsional vibration damping device.
Prior art torsional vibration damping devices are known, for example, from German Patent Application P 39 22 730.8. This reference discloses a clutch disk with a torsional vibration damping device having a hub disk arranged between two cover plates which are rotationally fastened together and held apart at a fixed distance by flat distance pieces. The cover plates can be rotated relative to the hub disk about the axis of rotation within limits which are determined by the circumferential size of apertures in the hub disk for the passage of the distance pieces. The radial distance of the distance piece from the axis of rotation is substantially determined by strength considerations and is balanced against weight and space requirements of the cover plates and hub disk. On the one hand, arranging the distance pieces at a distance from the axis of rotation which is as large as possible is desirable in order to keep the forces on the connections to the cover plates as small as possible. On the other hand, an increase in the radial size of the cover plates is not desirable with respect to weight and space requirement of the clutch disk.
When a minimum material thickness for the joint region of the distance pieces in the cover plates is taken into account, it follows that--in the current prior art--the apertures extending in the peripheral direction must be located outside the circumferential region of the spring elements. That is, the maximum twist angle of torsional vibration damping devices of the prior art is limited to the angular range between two spring elements.